When a bone fracture occurs, normal bony healing occurs in a series of stages. Initially, there is the formation of a hematoma (blood clot) between the fractured bone ends and some inflammation associated with the fracture. In the next stage of the healing process, there is then recruitment of fibroblast cells for producing collagen within the fracture gap. The collagen matrix forms the scaffolding upon which new bone will be deposited. During this phase, there is also in-growth of new capillaries (neovascularization), thereby providing a blood supply to the area. The combination of the blood clot with fibroblasts and new blood vessels creates what is often referred to as a “soft callous” of bone within the fracture site.
In approximately 6-8 weeks, the soft callous begins to calcify and harden, and a “hard callous” is formed across the fracture site. Long-term, there is remodeling of the hard callous, i.e. the remodeling re-arranges the microscopic architecture of the new bone so that it becomes identical to the surrounding bone. This process can continue for as long as a year following the fracture.
Several approaches for selective reconstruction of bones using distraction have been disclosed. For example, U.S. Pat. No. 5,067,954 to Ilizarov discloses an medical device for distraction based plastic reconstruction of a hand. U.S. Pat. No. 4,978,347 to Ilizarov discloses a distraction device for short tubular bones.
For example, distraction procedures may be applied to correct skeletal growth discrepancies between the maxilla (upper jaw) and mandible (lower jaw), which can be the result of congenital defects, abnormal development/growth, trauma, or pathology. When a discrepancy in growth between the jaws occurs, the result may involve morphologic changes that affect the patient's facial appearance and functional disturbances, such as a nonfunctional occlusal (bite) relationship. Significant malocclusions may be associated with difficulty eating/chewing, and speaking. In cases where there is severe mandibular or maxillary deficiency, the patient's airway may be compromised resulting in obstructive sleep apnea or respiratory distress.
In general, patients with significant skeletal facial deformities cannot be treated with orthodontic treatment alone. In cases where the patient requires orthognathic (corrective jaw) surgery, osteotomies are created within one or both jaws, the position of the mandible and/or maxilla is corrected, and rigid fixation is applied. Surgical treatment is typically carried out when the patient has reached or is approaching skeletal maturity, which occurs following puberty.
Despite the high success rates of orthognathic surgical techniques, there are specific cases where typical procedures to advance the mandible and/or maxilla cannot be utilized. One application is where the desired advancement is beyond what can be achieved with a conventional osteotomy, i.e. an advancement of greater than 12 mm, and another application is mandibular advancement during the neonatal period because the size of the mandible in a newborn would not allow for conventional bone cuts and skeletal movements. In both applications, the approach involves the creation of osteotomies and the application of a device that would allow for gradual distraction (advancement/lengthening) of the bone segments, i.e. distraction osteogenesis.
Several devices for mandibular distraction osteogenesis have been disclosed. For example, U.S. Patent Application No. 2007/0162045 to Ahmad discloses a mandibular distractor device comprising a screw based track. U.S. Pat. No. 6,113,599 to Landsberger discloses a mandibular distractor device comprising a rotatable hub, and a pair of threaded arms extending therefrom. Yet another mandibular distraction device device is disclosed in U.S. Pat. No. 6,322,566 to Minoretti et al. and comprises a pair of extendable arms for implantation in the jaw bone of the patient.
Nevertheless, the typical mandibular distractor device may have drawbacks. For example, in mandibular distraction procedures for infant patients, the device may require a tracheotomy to permit access for adjustment subsequent to surgical implantation. Moreover, during the original implantation, the initial incision needed for typical mandibular distractor devices is significant, which may result in more scarring and trauma for the patient.